Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.29   3.826%   $63.635   $63.64   $63.65   $63.60  
  Purchase #2 $36.26   5.694%   $38.3246   $38.32   $38.30   $38.30  
  Purchase #3 $126.90   7.623%   $136.5736   $136.57   $136.55   $136.60  
  Purchase #4 $221.70   6.213%   $235.4742   $235.47   $235.45   $235.50  
  Purchase #5 $63.67   6.557%   $67.8448   $67.84   $67.85   $67.80  
  Purchase #6 $163.77   10.632%   $181.182   $181.18   $181.20   $181.20  
  Purchase #7 $97.72   3.692%   $101.3278   $101.33   $101.35   $101.30  
  7 purchase totals = $771.31       $824.3620   $824.35   $824.35   $824.30